be careful totally bypassing the radiator cooler. Cold climes it actually warms up the trans to operating temp. most newer electronic controlled transmissions will not lock up till they get about 100 degrees. saves the converter. dodge even puts a heat transfer unit in the diesels in line before the radiator cooler, it then goes thru a air cooler before it returns to the pan.
get the the radiator checked, have the trans flushed and see how it goes.
sometimes it works, but in my exp., once a converter starts the shutter it will continue 75% of the time.
one last thing, is this just doing it when first warming up? if so replace the trans temp sensor.

and hes correct. the third generation toyota camrys are exactly like that. and those cars are some of the worst ones for flushing the transmission. the sensors read that cold fluid and it disengages torque converter lockup and reduces the pump pressure so it wont damage the pump and seals.

the old turbo 350/400 ford FMX, powerglides, fords C4 5 and 6, dodge 727s and the 904 transmissions will flush 14 quarts in about 3 minutes. those yotas........a minimum of 15. giant PITA.

torque converter shudder will damage it in the long run. i know the ford AOD trans that were used on the crown vics (mid 80s to the end of production) were notorious for the shaking when the fluid started breaking down. it lost the anti foaming properties and that caused air bubbles to form. then the air pockets in the fluid made the car jump like a long tailed cat in a room full of rocking chairs.

I had the same issue with my 2006 D40. I think I was about 120K. I honestly thought it was road construction and that's why the truck would "vibrate and jolt." Since then the radiator has been replaced with the supposed new part #. The tranny fluid has been drained and refilled multiple times (at least 4).. I don't drive her up many steep drives. Usually flat desert but stop around 200 miles in to let the temps cool a little. A trusted mechanic told me to pretty much "drive it until it fails." It's been almost 2 years since the initial issue and about 10K miles later. Still hauls ass but I don't accelerate crazy, ease into it, check fluids often. Everything else looks good.

I recently bought a 2007 4wd CC about 3 months ago with 118k on it .. and within a week i did the bypass.. its super easy and took literally 5mins.. there is enough hose underneath to loop the cooler together on the radiator and just use the external cooler that is mounted up above without having to buy any additional hose.. not sure i know what shutter you are talking about being this is my first automatic but i hope i dont have to run into that issue..have had my 95 for 12 years and my 98 for 6 .. so will see how this thing compares to those

Thank you everyone for your input, and I apologize for not posting for a long while.

In October I had the radiator replaced and the transmission flushed for a third time. When replacing the radiator, my mechanic said there was definite intermixing of fluids. I am frustrated that I wasn't more adamant about this issue earlier- I never saw the milkshake of death, the only sign was my transmission fluid changed a few shades lighter.

Since October the Frontier has been so-so. Some days I will experience some torque converter buzz if I'm heavy on the throttle while still in overdrive. My concern is the damage may have already been done and will progressively get worse. Transmission repair on these trucks is expensive- do I trade it in and lose money now, or hope that the transmission stays together for a few more years- or potentially be $3-5k out of pocket if it fails?

I am conflicted whether to keep the truck or trade it in and wash my hands of this mess- I have my eyes set on maybe purchasing a newer Wrangler with the 3.6L engine, or Toyota pickup/SUV... Maybe the closest models to a modern D21.

Nissan will not be receiving my return business- I know forums exasperate the number of issues that occur on certain vehicle models, but this particular issue cost me over $1,500, is well documented on the forums, left my vehicle in questionable condition and Nissan has not provided the appropriate service for an issue that occurs around the 80-120,000 mile mark.

Update December 27th, 2016: Traded the Frontier in, with 114,000 miles, for $10,000 trade in value.